Mercury cathode electrolytic cell



March 10, 1953 R. A. HORST MERCURY CATHODE ELECTROLYTIC CELL original Filed sept. 18,"1942 INVENTOR ROY A. HORST ATTORN Y Patented Mar. 1G, 1953 ITED STATES TENT OFFICE MERCURY CATHQDE ELECTROLYTIC CELL Roy A. Horst, Syracuse, N. Y., assignor to Allied Chemical & Dye Corporation, New York, N. Y., a corporation of New York (Cl. 20a- 220) 2 Claims.

This invention relates to the electrolysis of brine and is particularly concerned with a new and improved mercury cathode apparatus for the conduct of such electrolyses.

rlihis application is a division of my copending United States patent application Serial No. 458,844, filed September 18, 1942, now Patent Nq. 2,467,892.

In the past various types and designs of mercury cathode electrolytic apparatuses have been proposed.

An early apparatus is the type commonly known as the Castner cell. The Castner cell (U. S. Patent 518,135 of 1894) involves a pair of brine chambers in which brine is electrolyzed to form an amalgam and an intermediate washing chamber in which amalgam is washed with water to remove the active metal and regenerate or reclaim the mercury. The apparatus is so balanced and actuated that by tipping the apparatus rst in one direction and then in the other, the mercury is caused to flow from one brine chamber, through the washing chamber, to the second brine chamber and then back in the reverse direction. y

Later apparatus substituted stationary brine and Washing chambers at diierent levels and provided various types of elevators for conveying 'the mercury from the lower to the higher chamber. Such apparatus is illustrated by the Whit- Iing cell of U. S. P. 951,228 of 1910. The Whiting 'cell involved a brine chamber and a washing chamber situa-ted side by side. The brine chamber was arranged at a slightly higher elevation than the washing chamber so that mercury would flow by gravity from the former to the latter. A bucket-wheel elevator was provided for raising the mercury from the low elevation of the washing chamber to the higher elevation of the brine chamber.

The present invention is concerned with modications in apparatus of the latter general type, i. e., with electrolytic apparatus having a relatively high brine chamber and low washing chamber and an elevator for raising the mercury.

The apparatus of the invention is applicable to the electrolysis of salts of amalgam-forming metals in general but is especially applicable to the electrolysis of salts of the metals which ren act with Water, for example, the electrolysis of the chlorides and bromides of the alkali-metals. 'That chamber in which the metal salt is elec- 'ltrolyzed to form an amalgamof the free metal will be referred 'to' herein as the brine chamis washed from the amalgam, thus restoring the mercury to its initial condition, as the regenerator or, since when water is employed as the washing liquid, as is customarily the case, free hydrogen and metal hydroxide are formed, as the hydrogen or hydroxide chamber.

The cell of the invention is preferably at least lve times as long as it is Wide; i. e., the brine chamber mercury bed has a width not more than one-fifth its length. The brine chamber is provided with a plurality of cross-members or baiiles positioned on top of the anodes at more or less regular intervals to conne the now of brine primarily to the narrow space between the mercury cathode and the anodes disposed thereabove.

The abnormally long brine chamber and the baiiles so placed as to concentrate the iiow of brine in the zone between the anode and cathode cooperate to provide a high velocity of ow of brine in this zone. This high velocity of thebrine scours from the anodes the small bubbles of chlorine which normally tend to adhere to their surface. not only substantially improves the voltage efficiency of the cell but also tends to inhibit irregular erosion of the anodes and thus not only to further increase the voltage eiciency but at the same time to prolong the useful life of the anodes.

In order to secure the greatest advantage from the scouring effect of the brine, it is desirable to provide chlorine escape channels transverse to the flow of brine. This may be accomplished by provision of many spaced anodes, each fairly narrow, so that chlorine is provided with frequent passages for escape upwards between anodes, or it may be acomplished by slotting the anodes vertically to provide even more frequent channels. A preferred form of anode is deeply grooved on its underface to provide gas channels. Chlorine collecting in the channels finds its Way out at the ends of the anodes when it can escape to the gas space above. This escape may be still further facilitated by provision of one or more holes from each channel to the upper face of the anode. The grooved anodes have substantially greater rigidity and substantially less electrical resistance than anodes of comparable size in which slots are cut all the way through.

Another important feature of the apparatus of the invention is the provision of concurrent brine and mercury now, which in combination with the directing eiiect of the brine chamber bailes sweeps any foreign matter rapidly forward toward the outlet whence it may be removed When- The prompt removal of these bubbles ever the accumulation of such material is sucient to warrant it. Since the eciency of a mercury cathode electrolytic cell is substantially impaired by the accumulation of foreign material on the surface of the mercury in the zone of electrolysis, the rapid and efficient removal of such material from the zone of electrolysis contributes considerably to the electrical efciency of the cell.

The practical application of my invention is illustrated by the speciiic embodiment described in detail below in connection with the accompanying drawing, wherein Fig. 1 is a side elevation showing a specic embodiment of the invention. The apparatus is shown partly in sectional View and partly phantom View to show more clearly' the construction of the apparatus.

Fig. 2 is an enlarged cross-section on line A-A of Fig. l.

In the apparatus illustrated the cell comprises a brine chamber l and a regenerator chamber 2. By reference to Fig. 2 it will. be seen that the brine chamber is constructed as a long charnber comprising a steel shell 3 provided with a lining of concrete or other suitable material il.

For a cell having a capacity of about a hall metric ton of chlorine per day and a rated load of 16,6% amperes, chamber l may be in the neighborhood of 21/2 feet Wide by i0 feet long. As will be apparent from Fig. l, the floor of this chamber is a succession of steps and the depth of the chamber is accordingly somewhat greater at one end than at the other'. The floor of the brine chamber l may be constructed of` concrete or other alkali-resistant' materials of construction. A particularly suitable type of construction involves the use of a poured concrete lining supporting precast concrete working surfaces as more fully described in U. S. application Serial No. 458,847 led September 18, 1942, now abandoned.

A pair of channel-shaped steel structural members 5 form the sides' of the regenerator chamber. One side race of each channel provides a supporting surface for shell 3. The channel irons are separated from shell 3 by sealing gaskets t to prevent leakage of hydrogen from or air into chamberV 2. The' shell may be secured to the members c by' a series of bolts l. The iioor of regenerator chamber 2 has a gentle slope with its high end beneath the' lou1 end of charnber l and its low end beneath the high end oi chamber I. This slope', which is at the rate of about @is inch per linear foot, may be provided by a concrete fill S. The iioor of the regenerator chamber is preferably composed of compressed graphite sections e having vertical ns l@ run ning longitudinally of the chamber and providing channels for iiow of mercury from the high end of the regenerator chamber to the low end thereof as more clearly shown in Fig. 2, The ends of sections 9 may be beveled or notched, if desired, to provide transverse channels lea.

At the left end of the cell an elevator il, hich may be of the bucket-Wheel type, is provided for elevating mercury from the low end or" the regenerator to the high end of the brine chamber. At the opposite end of the cell a mercury seal construction i 2 is provided for permitting mercury to iiow from the brine chamber down to the upper end of the regenerator chamber.

Flow of brine in the cell illustrated is from left to right and the brine chamber is provided with a brine inlet conduit l and brine overlow and chlorine outlet conduitr lll. In the regenera-tor, ow of regenerating liquid, which is normally Water or dilute alkali-metal hydroxide when alkali-metal hydroxide is being produced, is also from left to right from inlet l to hydroxide overflow and hydrogen outlet iii.

The brine chamber i is provided with a remove able top or cover il supported on spacing elements or shirns i8. Spacing elements i8 prelerably are composed of a material having very little plasticity since the thickness of these elements determines the position of the anodes with respect to the mercury cathode. Leakage oi chlorine from the chamber between the cover l l and the lining. s may be avoided by applying a suitable caulking material 16a, such as putty, between the lining Il and the cover il.

The cover il is provided with a plurality ci apertures le, one for each anode. Projecting through apertures IS are a series of carbon anode supporting rods 2G to which the carbon anodes 2i are affixed in any suitable manner; they are shown threaded to the supporting rods. A shoulder of supporting rods 2i: may rest against the cover ll or may be separated therefrom by spacing washers 22 to initially adjust each anode so that its underface isV the desired distance from the mercury level in the cell. This distance may be in the neighborhood of l/l inch. The anode supporting rods 23 may be secured iirinly to the cover l? in any suitable manner, for instance by means of clamps or cement. The anodes 2l are graphite blocltsv which have a length substantially equal to the width of the brine chamber and normally have a Width about half of this. Their thicknessV may be around 3 inches initially and during the operative life of the anode gradually diminishes to about l inch.

I prefer to provide the anodes 2l with channels or grooves 23 disposed along the underface oi the anodes in a direction' substantially perpendicular to the flow of brine and mercury thereunder. These channels, while they may extend to the upper surface of the anodes, preferably extend initially about one-third of the way through and are connected with the space above the anodes by means of apertures 2li.

Electrical connection to the anodes is secured by means of electrically conductive supporting rods Zt* and metallic connectors 25 an bus bars 26. Connectors 25 may be :flexible or rigid and may be affixed to rod 2S by a stud bolt or a poured lead connection, or a clamp.

Electrical Contact between the current source and the mercury cathode is obtained through the shell 3 of the brine chamber; electrically conductive bus bar 2l is riveted or otherwise affixed to the shell preferably along its entire length in order to avoid voltage losses through the shell. Conductive rods 2S are welded to the shell 3 and project up to near the upper surface of the floor lining e. Mercury owing through the chamber iills the cups formed by the tops of these conductive rods and the lining and 'thus maires electrical connection with shell 3 and bus bar 2l.

Each anode 2l is provided with a baille 29 extending from the upper edge of the anode to a point above the level of brine in the brine chamber. These baffles may be aiiixed to the anodes in any suitable manner, for instance by means of dowels. Since the end of each anode and the accompanying baille present a Wall opposing the longitudinal flow of liquid through the cell, liquid is forced beneath the anodes and the primary ow takes place in the space between the lower anode surface and the mercury.

The regenerator chamber 2 is supplied with transverse bales 30 supported on pivots 3| in side walls and provided with operating handles 32 located outside the cell so that bales 3% may be manually raised to a horizontal position near the top of the regenerator. Suitable provision, such as valve-stem gaskets or washers, are provided to avoid leakage where handles 32 extend through the side wall 5 of the regener-ator. The normal operative position of baies 30 is as shown in the drawing with their lower edges resting upon fins I 0. In this position the baffles, which extend above the normal liquid level in the regenerator, force the liquid in flowing from inlet I5 to outlet I6 to pass under each baiile. This provides a progressive flow of the regenerating liquid essential for securing at the same time high alkali-metal hydroxide concentration and effective removal of alkali-metal from mercury.

It is not necessary that the baiiles be pivotally mounted for fixed baiiles would perform the function of preventing lengthwise diffusion of the regenerative liquid as well. The pivoted bales, however, facilitate cleaning as explained below.

A pair of outlets 33 and 34 have been shown at opposite ends of the cell. The outlet 33 preferably is disposed at approximately the mercury level in the cell when the cell is not operating; that is, when mercury in the upper chamber has all collected at the low end of the regenerator. This outlet has been shown as a simple capped pipe. Outlet 34, which is preferably disposed at about the normal mercury level when the cell is operating, is illustrated as a swivel type outlet which may be opened by swinging the high end to a point below the liquid level in the brine chamber.

For the production of highly concentrated alkali-metal hydroxide, it is desirable to limit heat loss by provision of suitable insulation. Since chamber I is so constructed that heat loss from this chamber is normally small, it is not necessary to provide additional insulation for this chamber. The primary loss of heat occurs at the seal end of the cell, particularly where mercury contacts the exterior metal walls of the unit. Thus, if the walls of mercury seal I2 are 'composed of metal considerable loss of heat at this point may occur unless adequate insulation is provided. It is also desirable to insulate side walls 5 of chamber 2 to conserve heat, particularly when caustic soda of about 50% concentration is being produced. Since the shell 3 loses some heat and is an active electrical conductor, it may be advantageously protected by a suitable material serving as both a heat and electrical insulator.

In assembling the above apparatus for operation, the unit is completely assembled and the required amount of mercury introduced with cover I1 removed. Anodes 2| are xed to the cover with suitable adjustment of distances so that when the cover is placed upon spacers IS, which may be up to 1%, inch thick or, in some cases, up to about 11/8 inches thick, the underfaces of the anodes are within about 126 of an inch of the mercury surface. Since it is desirable to avoid as much as possible working around the cell, there is an advantage in securing bus bar 2@ rigidly to the anodes and treating this bus bar as a part of the cover assembly. Battles 29 are affixed to the anodes 2l and the cover is then placed on spacing elements I8 of the aforementioned thickness. The cover I1 is then sealed in place by means of putty I8a.

To start operating the cell, elevator` II is set in operation to provide a sulcicnt flow of mercury through the cell so that the oor of the brine chamber is covered with a thin layer of mercury. Brine is introduced through inlet I3 until it begins to flow out through overflow outlet i4 and water is introduced at I5 until it begins to ow out through overflow outlet I6.

The following description illustrates the operation of the cell for the production of chlorine and aqueous 50% sodium hydroxide solution from sodium chloride brine:

Aqueous 25% sodium chloride solution is introduced at I3 at an hourly rate of about 355 liters and at a temperature of about 30 C. A sufficient voltage is applied between bus bars 26 and 2l to provide -a cathode current density of about 211/2 amperes per square decimeter. The flow of water into the regenerator chamber may be controlled to provide the concentration of sodium hydroxide desired, for example 50-52% NaOH. Under normal operating conditions with a cell of the type described, with elevator II and mercury seal I2 insulated to avoid heat loss, an adequate removal of sodium from the amalgam is secured in travel of amalgam from the mercury seal I2 to elevator II. Under these conditions of operation the unit is capable of producing in the neighborhood of 500 kilograms of chlorine gas and a corresponding lamount of 52% sodium hydroxide solution per day.

As the operation of the cell continues, the underfaces of anodes 2l are gradually worn or oxidized away and consequently the spacing between the mercury and the active anode surfaces increases. When this spacing has increased to about 1/2 inch, which may be after 2 to 6 months operation more or less, operation of the cell is discontinued and the spacing of the anodes is readjusted by removal of the required number of shims I8 to lower cover I'I and thus bring the active anode surfaces approximately to their original position. This adjustment may be coincided with the customary cleaning of the cell to remove any accumulation of foreign material from the anodes, the walls of the cell and from the mercury. For removing foreign material from the mercury, the arm on outlet 34 may be swung into a lower position to permit brine and foreign material to flow out through this outlet. For cleaning the regenerator chamber, baffles 36, if of the m-ovable type, are turned to inoperative position to permit washing liquid to flow freely along the oor and sweep any material which has accumulated thereon to the lower end of the chamber where it may be withdrawn through outlet 33. The wash water for this purpose may be introduced through outlet conduit I6 or through a wash liquid inlet specially provided for this purpose. When the cell has been properly cleaned, the outlets are closed, the cover is replaced, and the chambers relled with brine and water and operation started as before.

I claim:

1. An electrolytic cell of the mercury cathode type comprising a brine chamber having a substantially horizontal floor for the flow of mercury connected cathodically to a current supply, a top providing a closure for said chamber, at least one spacing element separating said top from said chamber and adapted by removal thereof to lower the top to a second lower position, substantially horizontal anodes suspended from said top and having upper surfaces spaced downwardly from said top, and having lower surfaces disposed above and in proximity to the floor of said `brine chamber, means for introducing mercury and brine at -ene 'end nf said Vcharnber so that the mercury flows over said oor beneath said lower surfaces, Vand the brine flows over the surface 4of the mercury, outlet means for withdrawing brine 'and mercury at the 'other end thereof, a series of transverse baies disposed at intervals along said chamber and extending from .the upper anode surfaces upward substantially .above said upper anode surfaces and above the brine outlet means and terminating below said top so ,as to confine the low of brine essentially to the space below said lower anode surfaces and so as to cause ow .of generated gas lengthwise of .said chamber in the space between said .baflies and said top, and means for removing gas from said last-named space.

2. An electrolytic cell as dened in claim 1 wherein each anode has its underface provided .REFERENCES CITED The Vfollowing references are of record in the 10 file of this patent:

`UNITED STATES PATENTS Number Name Date 2,104,678 Sorensen Jan. 4, 1938 FOREIGN PATENTS Number Country Date 17,415 Great Britain of -1898 22,406 Great Brita-in of 1900 '316,694 Great Britain Aug. 8, 1929 

1. AN ELECTROLYTIC CELL OF THE MERCURY CATHODE TYPE COMPRISING A BRINE CHAMBER HAVING A SUBSTANTIALLY HORIZONTAL FLOOR FOR THE FLOW OF MERCURY CONNECTED CATHODICALLY TO A CURRENT SUPPLY, A TOP PROVIDING A CLOSURE FOR SAID CHAMBER, AT LEAST ONE SPACING ELEMENT SEPARATING SAID TOP FROM SAID CHAMBER AND ADAPTED BY REMOVAL THEREOF TO LOWER THE TOP TO A SECOND LOWER POSITION, SUBSTANTIALLY HORIZONTAL ANODES SUSPENDED FROM SAID TOP AND HAVING UPPER SURFACES SPACED DOWNWARDLY FROM SAID TOP, AND HAVING LOWER SURFACES DISPOSED ABOVE AND IN PROXIMITY TO THE FLOOR OF SAID BRINE CHAMBER, MEANS FOR INTRODUCING MERCURY AND BRINE AT ONE END OF SAID CHAMBER SO THAT THE MERCURY FLOWS OVER SAID FLOOR BENEATH SAID LOWER SURFACES, AND THE BRINE FLOWS OVER THE SURFACE OF THE MERCURY, OUTLET MEANS FOR WITHDRAWING BRINE AND MERCURY AT THE OTHER END THEREOF, A SERIES OF TRANSVERSE BAFFLES DISPOSED AT INTERVALS ALONG SAID CHAMBER AND EXTENDING FROM THE UPPER ANODE SURFACES UPWARD SUBSTANTIALLY ABOVE SAID UPPER ANODE SURFACES AND ABOVE THE BRINE OUTLET MEANS AND TERMINATING BELOW SAID TOP SO AS TO CONFINE THE FLOW OF BRINE ESSENTIALLY TO THE SPACE BELOW SAID LOWER ANODE SURFACES AND SO AS TO CAUSE FLOW OF GENERATED GAS LENGTHWISE OF SAID CHAMBER IN THE SPACE BETWEEN SAID BAFFLES AND SAID TOP, AND MEANS FOR REMOVING GAS FROM SAID LAST-NAMED SPACE. 